Generally, fine pattern formation is carried out by the photolithography in manufacturing processes of a semiconductor device. A number of substrates called photomasks (hereinafter referred to as transfer masks) are normally used for this fine pattern formation. The transfer mask comprises generally a transparent glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the transfer mask.
In the manufacture of a transfer mask by the photolithography, use is made of a mask blank having a thin film (e.g. a light-shielding film or the like) for forming a transfer pattern (mask pattern) on a transparent substrate such as a glass substrate. The manufacture of the transfer mask using the mask blank comprises an exposure process of applying required pattern writing to a resist film formed on the mask blank, a developing process of developing the resist film according to the required pattern writing to form a resist pattern, an etching process of etching the thin film according to the resist pattern, and a process of stripping and removing the remaining resist pattern. In the developing process, a developer is supplied after applying the required pattern writing to the resist film formed on the mask blank to dissolve a portion of the resist film soluble in the developer, thereby forming the resist pattern. In the etching process, using this resist pattern as a mask, an exposed portion of the thin film, where the resist pattern is not formed, is dry-etched or wet-etched, thereby forming a required mask pattern on the transparent substrate. In this manner, the transfer mask is completed.
The transfer mask and the mask blank for manufacturing the transfer mask are cleaned when they are manufactured or used. Conventionally, an acid such as sulfuric acid is generally used for such cleaning (see, e.g. Patent Document 1).